Items that are packaged and stored for later use are often treated with an additive material to enhance, preserve, or otherwise modify the item for eventual sale or use as the modified item. In some embodiments, the additive material is deposited in a packaging container (e.g., storage bag or processing bag) with the item to be stored, such that over time or upon initiation of an item treating process, the additive material coats, penetrates, is absorbed by, or otherwise treats the stored item. In many cases, the deposited additive material (e.g., a liquid, powder, or gel) tends to pool or collect at the bottom of the container, resulting in a disproportionately large portion of the additive material being applied to a lower portion of the stored item, and a disproportionately small portion of the additive material being applied to an upper portion of the stored item. While this uneven treatment of the item may in some applications be reduced by filling the storage container with a larger amount of the additive material, this may result in the use of excess additive material within the storage container, with the excess material being discarded with the packaging (and not being applied to the stored item) upon removal and use of the item.